Many electronic devices include an audio output circuit for outputting an analogue audio signal to an accessory or peripheral apparatus that can be removably connected to the electrical device in use. For example, for many portable electronics devices a set of headphones or similar audio accessory may be removably connected to the device, to be driven by an analogue audio signal output from that device. FIG. 1 illustrates an electronic device 100, which will be referred to as the host device, that in use can be connected to an accessory audio apparatus 101, such as a headset, e.g. headphones or earbuds or the like. In use the accessory apparatus 101 may be removably connected to the host device 100 via a suitable connector, e.g. a mating connector such as plug and receptacle arrangement. One well known connector for audio accessories is a 3.5 mm jack plug and jack socket arrangement, whether a four pole (TRRS) or three pole (TRS) connector, but other connectors are known, such as USB type connectors, and may be used for analogue audio signals.
The host device 100 includes an audio output stage 102 for driving an audio load, such as a speaker 103, of an accessory apparatus 101 when connected. The audio output stage 102 may thus be connected to a contact or pole 104 of a connector of the host device 101, e.g. a jack socket, which is arranged to make electrical contact with a corresponding contact or pole 105 of a connector, e.g. jack plug, of a suitable accessory apparatus when connected. There is thus an audio signal path 106 between the output stage 102 and contact 104 of the connector.
Typically when not being used, e.g. without a suitable audio accessory apparatus connected, the audio output stage 102 is inoperative and typically the audio signal path 106 between the output stage 102 and contact 104 is clamped to ground. Switch 107 is thus provided so as to clamp the audio signal path to ground when closed and opened in use when driving an audio output signal to a connected accessory apparatus.